1. Field of the Invention
The invention relates to a television receiver with a video tape recorder integrally incorporated therein, the video tape recorder having recording and reproducing functions.
2. Description of the Related Art
In order to respond to various consumer needs due to recent increases in variety of life-style, a television receiver with a video tape recorder, which has recording and reproducing functions and is integrally incorporated therein, is becoming widespread.
Generally, such a television receiver with a video tape recorder has a configuration shown in FIG. 2.
A common terminal c of an external-input changeover switch 22 which functions as an external input terminal of a video tape recorder 21 is connected to a video signal recording circuit 25 and to one input terminal (R/EE terminal) a of a first changeover switch 24, via an automatic gain control (AGC) circuit 23 which adjusts the level of an input signal to a constant value. The output of a video signal reproducing circuit 26 is connected to the other input terminal (P terminal) b of the first changeover switch 24.
The video signal recording circuit 25 is a block which records a video signal on a recording medium 27 such as a video tape loaded into the video tape recorder 21. The video signal reproducing circuit 26 is a block which reproduces a video signal recorded on the loaded recording medium 27.
An external input terminal 32 to which a separate video tape recorder (not shown) or the like is to be connected is connected to one input terminal a of the external-input changeover switch 22. A radio frequency (RF) input terminal 28 to which a television antenna (not shown) or the like is to be connected is connected to the other input terminal b of the external-input changeover switch 22, via a tuning circuit 29, an intermediate frequency (IF) amplifier circuit 30, and a detection circuit 31.
A common terminal c of the first changeover switch 24 is connected to a television signal processing circuit 33. A video signal output of the television signal processing circuit 33 is supplied to a cathode ray tube (CRT) 34, and an audio signal output of the circuit to a loudspeaker 35.
In the thus configured television receiver with a video tape recorder, when a video signal reproduced from a recording medium such as a video tape by the separate video tape recorder connected to the external input terminal 32 is to be input, the common terminal c of the external-input changeover switch 22 is connected to the input terminal a of the changeover switch 22. Also, the common terminal c of the first changeover switch 24 is connected to the input terminal a of the changeover switch 24.
As a result of the connection, the video signal reproduced by the separate video tape recorder is supplied via the external input terminal 32 and the terminals a and c of the external-input changeover switch 22, to the AGC circuit 23. The input signal is adjusted so as to have a constant level at which the signal can be recorded, and then supplied to the video signal recording circuit 25 and the input terminal a of the first changeover switch 24.
When the video tape recorder 21 is in the recording mode (dubbing mode), therefore, the video signal reproduced by the separate video tape recorder is recorded on the loaded recording medium 27.
Whether the recording mode is set or not, the reproduced video signal is supplied to the television signal processing circuit 33 via the terminals a and c of the first changeover switch 24, to be subjected to a predetermined process. The processed signal is then supplied to the cathode ray tube 34 and the loudspeaker 35.
In other words, when a video signal reproduced from the recording medium by the separate video tape recorder is input via the external input terminal 32, the reproduced video signal is supplied via the AGC circuit 23 to the television signal processing circuit 33 whether the video tape recorder 21 is in the recording mode or not.
The AGC circuit 23 generally detects the level of the horizontal synchronizing signal and adjusts the detected horizontal synchronizing signal so as to have a constant level, thereby adjusting the input signal to a constant level at which the signal can be recorded (this level is set to be 1 V.sub.p-p).
Incidentally, as video tape recorders have become widely used, the problem of unauthorized duplication of a video tape has been given a great deal of attention. Recently, therefore, a video tape which has been subjected to a so-called copy protection processing has been made available in order to protect against such unauthorized duplication.
In the copy protection processing, a pulse-like signal is superposed in the horizontal synchronizing signal portion of a video signal recorded on a video tape, so that the horizontal synchronizing signal is forcedly changed in level. When a video signal on which such a processing has been conducted is processed by the AGC circuit 23, the resulting signal does not meet standards. When such an out-of-standard video signal is reproduced, the reproduced image is very unclear (or it is substantially filled with noise).
In the above-described television receiver with a video tape recorder, when a copy-protected reproduced video signal is supplied from the separate video tape recorder connected to the external input terminal 32, the reproduced video signal must be passed through the AGC circuit 23 of the video tape recorder 21. Even in the case where the reproduced video signal is merely displayed on the television receiver, therefore, there arises a problem in that the television receiver displays only a very unclear image.
In other words, when a copy-protected video signal which is reproduced by the separate video tape recorder is displayed on the above-described conventional television receiver, the resulting image is very unclear, thereby producing a problem in that it is impossible to view the image. This problem is produced also in the case where a copy-protected television signal is transmitted by radio waves and then received via the RF input terminal 28.